The synthesis of various multi-arm radial or star polymers has grown in both practical and theoretical interest in a variety of industries. More particularly, the synthesis of well-defined star polymers having a readily determinable, definite number of arms have become increasingly important over the years. Certain star polymers are useful as, inter alia, surfactants, lubricants, rheology modifiers, viscosity modifiers, control agents, coatings and sealants. Others may be used as thermoplastic elastomers for a variety of applications.
To date, there has not been a successful synthesis of a block copolymer or star polymer having at least one polyisobutylene (PIB) block and at least one polyacrylonitrile (PAN) block, that is, a polyisobutylene-block-polyacrylonitrile copolymer, (PIB-b-PAN). Polyisobutylene and polyacrylonitrile are highly incompatible polymers. By incompatible, it is understood that polyisobutylene and polyacrylonitrile have very different thermodynamic properties. For example, polyisobutylene has a glass transition temperature (Tg) of −61.2° C., while polyacrylonitrile has a Tg of +81.3° C. Since polyisobutylene is hydrophobic while polyacrylonitrile is hydrophilic., finding a solvent in which both polymers are soluble is not intuitive. Many non-polar solvents suitable for dissolving polyisobutylene are not suitable for dissolving polyacrylonitrile, anc vice versa. Polyacrylonitrile is such a unique substance, that the polymer is even insoluble in its own monomer, acrylonitrile.
Matyjaszewski, U.S. Pat. No. 5,763,948 teaches atom transfer radical polymerization (ATRP) as a method of synthesizing low polydispersity (Mw/Mn) block copolymers via anionic polymerization. That patent discloses, at least theoretically, the possibility of a copolymer having both acrylonitrile monomers and isobutylene monomers. However no solvent or system of solvents is disclosed therein in which polyisobutylene, polyacrylonitrile and acrylonitrile monomers are simultaneously soluble. Finally, there is no disclosure of how to make a PIB-b-PAN block copolymer inasmuch as there is no appreciation that a specialized solvent is necessary in which to carry out such polymerization.
Hence in light of the absence in the prior art of both (a) a method of synthesizing through ATRP a low polydispersity PIB-b-PAN copolymer, and (b) a suitable solvent in which polyisobutylene and polyacrylonitrile are simultaneously soluble, the need for such a copolymer and such a solvent is evident.